1. Field of the Invention
The present invention relates to a zoom lens unit and an image pickup apparatus which utilize an electrostatic actuator to drive a lens, and in particular, to a zoom lens unit and an image pickup apparatus which utilize an electrostatic actuator independently controlling and driving individual movable sections in which lenses are provided.
2. Description of the Related Art
In recent years, many efforts have been made to incorporate a camera unit with a zoom function into a mobile apparatus such as a cellular phone. In such a camera unit, a lens is driven along an optical axis to adjust a focus to finally form an image on a sensor. Attempts have been made to use an electrostatic actuator as a driving source that drives the lens across the optical axis.
In a zoom lens unit, lenses are independently driven to adjust the zoom scale factor of a lens system. In a zoom lens unit utilizing an electrostatic actuator, the electrostatic actuator comprises a stator and first and second movable sections. The first and second movable sections hold the respective lenses and are independently driven.
The stator comprises a driving electrode substrate and a holding electrode substrate mounted on the opposite inner surfaces of a stator frame. Further, the first and second movable sections are arranged so that there is a gap of several μm between each movable section and the corresponding one of the paired electrode substrates. The first and second movable sections are reciprocated between the paired electrode substrates and also moved along the axial direction of the lenses. The holding electrode substrate is provided with a first holding electrode used to hold the first movable section and a second holding electrode used to hold the second movable section.
A zoom lens unit configured as described above is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-126009 and the corresponding U.S. patent application Ser. No. 10/672,409, filed Sep. 29, 2003, Koga et al. In these documents, the first and second movable sections are electrostatically driven by using as switching circuit to supply voltages to the electrodes of the paired electrode substrates of the stator in a predetermined order. In the conventional zoom lens unit, with one of the movable sections held by the holding electrode substrate, voltages are supplied to the driving electrode substrate in a predetermined order to drive the other movable section. Thus, the conventional zoom lens unit can only alternately move the plurality of movable sections.
In the zoom lens unit, to change the zoom scale factor, each lens must trace a zoom curve based on a particular lens design. If the zoom curve is traced, it is not preferable that lenses from different groups be alternately driven. Alternately driving the lenses unavoidably causes the positions of a plurality of movable sections to be temporarily shifted from the zoom curve. That is, a subject gets out of focus during the zoom operation, resulting in a blurred image.